Alignment of semiconductor wafers and other articles

ABSTRACT

A wafer or some other article is aligned while being held by an end-effector.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to alignment of semiconductorwafers and other articles.

[0002] Fabrication of integrated circuits from a semiconductor waferinvolves many processing steps, and the wafer may have to be aligned asit goes from one step to the next. For example, before a wafer is diced,it has to be attached to an adhesive film stretched over a frame, whichrequires accurate alignment of the wafer to the frame. Alignment isperformed using a piece of equipment called aligner. A robot picks upthe wafer and places it on the aligner. The aligner adjusts the positionof the wafer in the horizontal plane to cause the center of the wafer tooccupy a predetermined position. Then the aligner rotates the wafer toplace the wafer into some predetermined rotational orientation, i.e.with some feature (a notch or a flat) on the wafer's circumference in apredetermined position. Then the robot picks up the wafer again andcarries the wafer to a target station for the next processing step.

SUMMARY

[0003] Some embodiments of the present invention eliminate the need touse an aligner. The wafer is aligned while held by the robot. The waferprocessing becomes faster and more economical, and throughput isincreased. Also, the wafer damage is reduced due to elimination of thewafer transfer to and from the aligner. In addition, the wafer positionis more precise at the target station because the positioning errorsinvolved in the robot picking up the wafer from the aligner areeliminated.

[0004] The invention is not limited by the embodiments and advantagesdescribed above, but is defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is a block diagram illustrating a wafer processing systemaccording to one embodiment of the present invention.

[0006]FIGS. 2, 3 are perspective views of a robot's end effectoraccording to one embodiment of the present invention.

[0007]FIG. 4 is a perspective and cross sectional view of a portion ofthe end effector of FIGS. 2, 3.

[0008]FIG. 5 is a cross sectional view of the end effector of FIGS. 2,3.

[0009]FIG. 6 is a perspective view illustrating an alignment operationaccording to one embodiment of the present invention.

[0010] FIGS. 7-9 are top views illustrating an alignment operationaccording to one embodiment of the present invention.

[0011]FIG. 10 is a perspective view illustrating an alignment operationaccording to one embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0012] In FIG. 1, a semiconductor wafer 120 is being transported from astation 121 to a station 122 by a robot 124. The wafer is being held bythe robot's end effector 130 attached to the robot's arm 134. Arm 134 isattached to a robot body 124B which itself may include a number ofmoving arms. In one example, end effector 130 is attached to a robot oftype GBY7S available from Genmark Automation of Sunnyvale, Calif. Therobot is controlled by its computer 140, which in turn may receivecommands from, and send information to, a programmable logic controller(PLC) 150. Computer 140 and PLC 150 are controlled by software of thepresent invention. The invention is not limited to any particular robotor robot control mechanism.

[0013] Stations 121, 122 can be any stations involved in wafer storageor processing. Examples include wafer storage cassettes, horizontalwafer shipment containers (“pods”), etch and deposition equipment, filmframe machines that attach adhesive film frames to wafers, dicingequipment. Before the wafer is placed on station 122, it is aligned atstation 170. Alignment involves adjusting the XY position and therotational orientation of the wafer relative to end effector 130. Seee.g. the following U.S. Pat. Nos. 6,164,894; 5,456,179; 5,452,078. Thewafer is aligned in end effector 130. Alignment station 170 does notneed a wafer holder or a platform to hold the wafer. The end effectordoes not need to release the wafer to perform the alignment.

[0014]FIG. 2 is a perspective view showing a top and a side of oneembodiment of end effector 130. FIG. 3 shows the same side and thebottom. FIG. 4 shows a vertical cross section of a portion of the endeffector along a line IV-IV in FIG. 2. FIG. 5 shows how a verticalcross-section might look along a line V-V in FIG. 2 (FIG. 5 is not anaccurate representation of some features as noted below). FIGS. 6-10illustrate a wafer alignment operation at station 170.

[0015] In the embodiment of FIGS. 2-5, the end effector is a non-contacttype. It holds the wafer with gas vortices emitted from openings 210(FIGS. 3, 5) in its flat bottom surface. Only a few of the openings arelabeled in the drawings. Gas vortex end effectors are described in U.S.Pat. No. 6,095,582 issued Aug. 1, 2000 to Siniaguine et al. andincorporated herein by reference. See also U.S. patent application Ser.No. 09/632,236 filed Aug. 4, 2000 by S. Casarotti et al.; U.S. patentapplication Ser. No. 09/633,086 filed Aug. 4, 2000 by S. Kao; U.S.patent application Ser. No. 09/877,366 entitled “Article Holders thatUse Gas Vortices to Hold an Article in a Desired Position”, filed Jun.8, 2001 by S. Kao. The end effector of FIGS. 2-5 has a body 220 made ofa top plate 220T and a bottom plate 220B. A number of vortex chucks 230(FIG. 5) are positioned in a hollow region between the two plates. Eachopening 210 is an opening of one such chuck. (FIG. 5 does not accuratelyrepresent the chucks' position.) A tangential passage 232 in the chuck'scylindrical sidewall enters the chuck tangentially to the sidewall. Gassupplied under pressure through a passage in arm 134 and an opening 240enters the chucks through passages 232. The chucks' sidewalls shape thegas flow in each chuck into a vortex. The vortices exit through openings210 and create an attraction force that draws the wafer towards the body220. At the same time, the gas creates a cushion that prevents the waferfrom touching the body 220.

[0016] Top plate 220T has a central portion 250 (FIG. 4) and aperipheral portion 260. Peripheral portion 260 extends sidewise from thebottom of central portion 250 and forms a horizontal shelf surroundingthe central portion 250. A ring 270 rotates around the end effector'sbody 220. Ring 270 has a horizontal portion 270H which slides over theshelf 260. Teflon strip or strips 280 (FIG. 4) are attached to the topsurface of shelf 260 and/or the bottom surface of the ring's horizontalportion 270H to reduce friction between the ring 270 and the shelf 260.Vertical portion 270V of ring 270 surrounds the end effector body 220.

[0017] Spring steel plates 310 are attached to the top surface ofcentral portion 250 with bolts 320 (FIG. 2). Bolts 320 are inserted intoholes 322 (FIG. 4) each of which passes through central portion 250 andterminates inside bottom plate 220B. Each plate 310 physically contactsthe top surface of the ring's horizontal portion 270H. The frictionbetween plates 310 and the ring's horizontal portion 270H prevents thering from rotating uncontrollably around body 220 but allows the ring tobe rotated at alignment station 170.

[0018] Ring 270 has outward protrusions 330. A pad 340 (FIGS. 3,5) isattached to the bottom surface of each outward protrusion. Wafer 120 ispressed against these pads 340 when drawn to the end effector by the gasvortices or other forces (depending on the type of the end effector).The friction between the pads and the wafer prevents the wafer fromunintentionally sliding horizontally relative to the end effector. Thisfriction also causes the wafer to rotate when the ring 270 isrotationally driven at alignment station 170.

[0019] At station 170, the wafer is moved in the end effector to causethe center of the wafer to coincide with the center of the end effector(we will refer to this stage as “XY positioning”). Then the wafer isrotated in the end effector to align the wafer rotationally. The XYpositioning involves techniques similar to those described in U.S.patent application attorney docket no. M-11881 US, entitled “ArticleHolders and Article Positioning Methods”, filed by A. J. Berger and F.E. Kretz on the same day as the present application and incorporatedherein by reference. The XY positioning involves the robot pushing thewafer against an object or objects. The wafer slides on pads 340 withoutthe end effector losing hold of the wafer. One embodiment is illustratedin FIGS. 6-9. FIG. 6 is a perspective view, and FIGS. 7-9 are top views.Here the objects against which the wafer is pushed are two sets ofvertical pins. One set of pins consists of pins 510.1, 510.2, 510.3,510.4 (“pins 510”). The other set consists of pins 520.1, 520.2, 520.3,520.4 (“pins 520”). Pins 510, 520 are mounted on a support plate 530.Pins 510 are positioned along a circle 540 (FIG. 7) of the same radiusas wafer 120. Pins 520 are positioned along a circle 550 of the sameradius as wafer 120. Pins 510.1, 510.2 are symmetric to pins 510.4,510.3 with respect to a horizontal axis 560. Pins 520.1, 520.2 aresymmetric to pins 520.4, 520.3 with respect to the same axis 560.

[0020] If wafers may have notches or flats, the pins are positioned sothat any two of the pins are farther apart than the maximum lateraldimension of the notch or flat. (This is just an exemplaryimplementation which does not limit the invention. In other embodiments,the pins may be positioned closer to each other than the length of aflat for example.)

[0021] As shown in FIGS. 6, 7, the end effector brings the wafer 120 tostation 170 with the wafer above the pins 510, 520, and the end effectorlowers the wafer so that the wafer is positioned between the pins,without touching the pins. The end effector's center CE is positioned ata predetermined point on axis 560. The wafer's center CW may be shiftedrelative to the end effector's center CE due to a positioning error. Themaximum error is determined by a particular application, and may be afunction of maximum positioning errors at source station 121. We willassume, for the sake of illustration, that the maximum positioning errorEmax of the wafer in the end effector at the stage of FIG. 6, i.e. themaximum distance between the centers CE and CW, is 1.25 mm. The wafer ispositioned so that it does not touch the pins 510, 520 when the error isnot more than 1.25 mm.

[0022] As shown in FIG. 8, the end effector moves to the left along axis560 to bring the wafer in contact with pins 510. The pins push the waferinto the circle 540. The wafer slides on the end effector pads 310 andchanges its position relative to the end effector until the waferposition coincides with circle 540. In this position, the wafer contactsall of pins 510, or it may contact three of pins 510 with the forth pinbeing against the wafer's notch or flat. To insure that the waferbecomes positioned in circle 540, the center CE of the end effector ismoved to the left of the center of circle 540 by the distance Emax=1.25mm or more, for example, 25 to 51 mm. (In FIG. 7, the center of circle540 coincides with the center CW of wafer 120.)

[0023] As shown in FIG. 9, the end effector now moves to the right alongaxis 560. The end effector's center CE moves along the axis into thecenter of circle 550. Wafer 120 comes in contact with at least three ofpins 520. Pins 520 steer the wafer into circle 550 as the wafer slideson pads 310. Now the wafer's center CW coincides with the end effector'scenter CE.

[0024] As shown in FIG. 10, station 170 also includes a motor 610 (e.g.a computer controlled stepper or servo motor) which rotates a wheel 620.After the stage of FIG. 9, the end effector moves into a position inwhich an edge of wheel 620 physically contacts the top surface of thering's horizontal portion 270H, causing the ring to rotate. A sensor 630scans the edge of the rotating wafer 120 and provides signals to thecomputer (not shown) controlling the motor 610. The signals indicatewhether the sensor has detected a notch, a flat, or some other alignmentmark on the wafer. Responding to these signals, the computer controlsthe motor 610 to position the wafer into a desired rotationalorientation relative to the end effector. Suitable sensors and motorcontrol algorithms are described, for example, in U.S. Pat. Nos.6,164,894 (issued Dec. 26, 2000), 5,456,179 (issued Aug. 13, 1996),5,452,078 (issued Sep. 19, 1995), all incorporated herein by reference.

[0025] When the alignment has been completed, the end effector placesthe wafer on destination station 122 (FIG. 1).

[0026] The invention is not limited to any particular number of pins510, 520, or their positioning. The pins do not have to be positionedsymmetrically with respect to any axis. Also, article 120 and endeffector 130 do not have to be round or symmetric. The pins can bereplaced by other objects, vertical or otherwise, as described in theaforementioned U.S. patent application attorney docket no. M-11881.Either pins 510 or pins 520 can be omitted in some embodiments. Theinvention is not limited to any particular positioning of pins 510, 520,motor 610 or sensor 630 relative to each other. The sensor may bepositioned close to the motor, below the motor for example.

[0027] In some embodiments, the XY positioning operations of FIGS. 6-9are omitted if the XY positioning errors are within the allowabletolerances.

[0028] The invention is not limited to any particular alignmentmechanism at station 170. For example, motor 610 can be coupled to endeffector 130 using some other coupling means than wheel 620. Sensor 630may be a through-beam type, a retroreflective type, a CCD camera, orsome other type, known or to be invented.

[0029] In some embodiments, station 170 is part of robot 124 ordestination station 122. For example, sensor 630, motor 610, and/orwheel 620 can be attached to the end effector or some other part of therobot.

[0030] Spring steel plates 310 allow ring 270 and wafer 120 to move uprelative to end effector body 220 if the end effector presses the waferagainst some surface at station 122. The surface may be that of a stickytape, e.g. a dicing tape. See the aforementioned U.S. patent applicationSer. No. 09/632,236 filed Aug. 4, 2000 by S. Casarotti et al., entitled“Detection and Handling of Semiconductor Wafers and Wafer-Like Objects”,incorporated herein by reference. Spring steel plates 310 allow the ringand the wafer to yield when the wafer is pressed against the surface, sowafer damage is avoided. The invention is not limited to any particularnumber or position of plates 310 Plates 310 can be made of a materialother than spring steel, or can be omitted.

[0031] The invention is not limited to any particular structures ormaterials. For example, strips 280 (FIG. 4) can be made of somethingother than Teflon, or may be omitted or replaced with other frictionreducing devices (e.g. bearings). Outward protrusions 330 on ring 270can be omitted. Pads 340 can be positioned elsewhere on the ring'sbottom surface. The invention is not limited to the presence of shelf260 in the end effector's body, or to any particular shape of the endeffector, or any particular coupling between the end effector body 220and ring 270. Ring 270 may be replaced with some other rotationalmember, for example, a half-ring or a number of rotational armsextending from arm 134. The ring or other member need not surround thebody 220. The ring may be positioned under the body. In someembodiments, ring 270 is omitted. The entire end effector 130 isrotatable on arm 134 around a vertical axis passing through the endeffector and/or the center of the wafer. The end effector may be anon-vortex type. For example, the end effector may hold the wafer with anon-vortex gas flow using the Bernoulli effect. The end effector may beof a vacuum type. If the end effector has a rotatable ring 270, gasinlets for creating the vacuum may be located on the bottom of ring 270.The end effector may also hold the wafer with electrostatic or magneticforces, with a mechanical clamp, or by other means, known or to beinvented. The wafer may be positioned above the end effector.Non-horizontal positioning of the wafer and the end effector is withinthe scope of the invention.

[0032] The invention is not limited to semiconductor wafers. Article 120may be include a stack of wafers bonded together to provide verticalintegrated circuits. See U.S. Pat. No. 6,184,060 issued Feb. 6, 2001 toO. Siniaguine and incorporated herein by reference. The article mayinclude a combination of semiconductor and non-semiconductor wafers. SeeU.S. patent application Ser. No. 09/791,977 filed on Feb. 22, 2001 by O.Siniaguine and incorporated herein by reference. In other embodiments,the article is a flat-panel display or some other type extendinggenerally along a plane.

[0033] The invention is not limited to end effector article holders.Holder 130 may be a hand-held article holder. A human operator may alignthe wafer in the end effector by pushing and rotating the wafer with theoperator's hand. The operator's hand may push the wafer or the ring 270or both. Holder 130 may also be part of non-electronically-controlledequipment. Other embodiments and variations are within the scope of theion, as defined by the appended claims.

1. An article alignment method comprising: holding an article with anarticle holder; and rotating at least a portion of the article holderaround an axis passing through the article to rotate the articlerelative to the article holder while the holder is holding the article.2. The method of claim 1 wherein holding the article comprises pressingthe article against the holder; and rotating at least a portion of thearticle holder comprises rotating at least a portion against which thearticle is pressed.
 3. The method of claim 2 wherein the article holdercomprises one or more openings through which one or more gas flows areemitted towards the article to attract the article to the holder; andthe article is pressed against one or more protrusions on the holder. 4.The method of claim 2 wherein the article is pressed against one or moreprotrusions on the holder; and the method further comprises pushing thearticle against one or more objects to cause the article to slide on theone or more protrusions while the holder is holding the article.
 5. Themethod of claim 1 further comprising transporting the article holder,with the article in the holder, to a rotary drive; wherein the rotatingoperation comprises coupling the drive to the article holder to transfera rotary motion of the drive to the article.
 6. The method of claim 5wherein coupling the drive to the article holder comprises coupling thedrive to a rotational member of the article holder, the rotationalmember physically contacting the article and coupling the rotary motionof the drive to the article.
 7. A method for article handling, themethod comprising: picking up an article with an article holder;sensing, with a sensor, the article's rotational orientation relative toan axis passing through the article, and if the rotational orientationis different from a predetermined orientation, then rotating the articleto place the article into the predetermined orientation, wherein thesensing and rotating operations are performed while the article is heldby the holder.
 8. The method of claim 7 wherein holding the articlecomprises pressing the article against the holder; and rotating thearticle comprises rotating at least a portion of the article holderagainst which portion the article is pressed.
 9. The method of claim 8wherein the article holder comprises one or more openings through whichone or more gas vortices are emitted towards the article to develop anattraction force attracting the article to the holder; and the articleis pressed by the attraction force against one or more protrusions onthe holder.
 10. The method of claim 8 wherein the article is pressedagainst one or more protrusions on the holder; and the method furthercomprises pushing the article against one or more objects to cause thearticle to slide on the one or more protrusions while the holder isholding the article.
 11. The method of claim 7 further comprisingtransporting the article holder, with the article in the holder, to arotary drive; wherein the rotating operation comprises coupling thedrive to the article holder to transfer a rotary motion of the drive tothe article.
 12. The method of claim 11 wherein coupling the drive tothe article holder comprises coupling the drive to a rotational memberof the article holder, the rotational member physically contacting thearticle and coupling the rotary motion of the drive to the article. 13.A robot end effector comprising a member rotational relative to the endeffector, to allow an article held in the end effector to rotate aroundan axis passing through the article.
 14. The end effector of claim 13wherein the end effector further comprises: a body to which the memberis coupled and around which the member is rotational; and a device forpressing the article against the member when the end effector is holdingthe article.
 15. The end effector of claim 14 wherein the devicecomprises a vortex chuck to emit a gas vortex towards the article. 16.The end effector of claim 15 wherein the vortex chuck is mounted in thebody.
 17. A robot end effector comprising a mechanism for holding anarticle and rotating the article around an axis passing through the endeffector.
 18. The end effector of claim 17 wherein the end effectorfurther comprises: a body to which the member is coupled and aroundwhich the member is rotational; and a device for pressing the articleagainst the member when the end effector is holding the article.
 19. Theend effector of claim 17 wherein the device comprises a vortex chuck toemit a gas vortex towards the article.
 20. The end effector of claim 19wherein the vortex chuck is mounted in the body.
 21. A computer systemprogrammed to control an article holder and a motor for rotating atleast a portion of the article holder to perform the operations ofclaim
 1. 22. A computer readable medium comprising computer instructionsto control an article holder and a motor for rotating at least a portionof the article holder to perform the operations of claim
 1. 23. Acomputer system programmed to control an article holder and a motor forrotating at least a portion of the article holder to perform theoperations of claim
 8. 24. A computer readable medium comprisingcomputer instructions to control an article holder and a motor forrotating at least a portion of the article holder to perform theoperations of claim 8.